Refrigerated liquid storage tank



A ril 29, 1952' F. J. ZAMBONI 2,594,603

REFRIGERATED LIQUID STORAGE TANK Filed July 25. 1949 3 Sheets-Sheet lim/ ai,

. :4 a/viy A ril 29, 1952 F. J. ZAMBONI REFRIGERATED LIQUID STORAGE TANKFiled July 25, 1949 3 Sheets-Sheet 2 :QTTOENEY Ap 1952 F. J. ZAMBONI2,594,603

. REFRIGERATED LIQUID STORAGE'TANK Filed July 25, 1949 3 Sheets-Sheet 5Patented Apr. 29, 1952 UNITED STATES PATENT OFFICE REFRIGERATED LIQUIDSTORAGE TANK Frank J. Zamboni, Hynes, Calif.

Application July 25, 1949, Serial No. 106,513

Claims.

The present invention relates to refrigerated storage tanks, and morespecifically to a tank particularly designed for refrigerating andstoring milk at dairy farms or other milk-producing centers until thesame can be picked up by tank truck for delivery to the creamery ordairy. Such tanks are usually quite sizeable, and may range up toseveral thousand gallons of capacity.

Owing to the extremely perishable nature of milk and the exactingstandards that prevail in the dairy industry throughout most of thecountry, it is necessary to chill the milk immediately from body heat toapproximately 40 F., and then hold the milk at 40 until it is picked upby the tank truck. The milk may be collected from several milkingsduring the day, and at each milking, a large volume of warm milk isadded suddenly to the previously collected milk which has been chilledto 40 F. One of the problems with which the present invention isconcerned is that of providing a refrigerating system capable ofhandling the severe load imposed by the sudden addition of severalhundred gallons of warm milk to the tank, with no more thaninsignificant rise in temperature of the milk already in the tank. Theprimary object of the invention, therefore, is to provide a new andimproved refrigerated tank capable of chilling a large volume of warmmilk almost instantly to the desired holding temperature as the milk ispoured into the tank, and thereafter holding the milk at a substantiallyconstant, predetermined temperature.

A number of novel features in the present invention contribute to theattainment of this object. For one thing, in the preferred form of myinvention the tank is made with inner and outer walls which are spacedapart by a refrigerant pipe wound around the inner tank wall. The pipeis interrupted at intervals along its length to provide a plurality ofshorter sections, each of which is closed off from its adjoiningsections, and each section being provided with its own refrigerantliquid line and suction line. This arrangement provides the necessarylength of refrigerant pipe required to handle the heat transfer load,but without the excessive pressure drop which would result if the pipewere made continuous, with a single liquid line and a single suctionline.

Another factor contributing substantially to the efficient transfer ofheat from the milk to the refrigerating equipment is the use of aliquid, such as water or brine, to fill the space between the inner andouter walls of the tank and to conduct the heat more rapidly anduniformly from the entire area of the inner wall to the entire area ofthe refrigerant pipe; the said liquid being preferably circulatedthrough the spiral channel defined between adjacent coils of the pipeunder conditions such that the pressure of the fluid against the sidewalls of the tank is al ways below the static head. In the preferredform of the invention, the pressure of the fluid is reduced to such anextent that the pressure at all points is subatmospheric, so that thewalls are pressed together by atmospheric pressure and held firmlyagainst the spacers between them. This is an important feature, as iteliminates the need for welding or otherwise tying the spacers to theside walls so as to hold the latter together.

To the best of my knowledge, all prior doublewalled refrigeration panelsor tanks having a liquid medium circulating therein have beenconstructed with internal spacers to which the side walls have beenwelded or otherwise tied, and the circulation of fluid has beenaccomplished by pumping the fluid under a positive pressure through thepassages between the spacers. The increased fluid pressure necessary toovercome the frictional losses due to circulation tends to spread thewalls apart, with the result that the welds between the walls andspacers are constantly placed under tension and frequently fail. In thepresent invention, circulation of the liquid medium is obtained byapplying a suction at one end of the passage, while the other end of thepassage is supplied with liquid at atmospheric pressure. As a result ofthis arrangement, the pressure exerted by the fluid against the walls isdiminished during circulation, and the side walls are pressed togetheragainst opposite sides of the spacers by atmospheric pressure, insteadof being pulled apart. Another object of the invention, therefore, is toprovide a refrigerated tank of the class described, wherein therefrigerant pipe or other spacer is attached for support solely at itsends to the inner wall of the tank, and all welds between the side wallsand the pipe or spacer are eliminated except at the extreme ends of thepipe. In practice, it may be desirable to tack weld the refrigerant pipeor spacer to the inner wall of the tank at five or six points along itslength, in order to facilitate assembly of the tank, but these weldsserve no particular structural function after the tank has beencompleted. Accordingly, it is to be understood that any claims directedto this feature are not avoided by merely tack welding the spacer to onewall of the tank at points intermediate its ends, where such tack Weldsserve no useful function in the completed tank, such as to hold thewalls of the tank to the spacer.

A'further object of the invention is to provide novel and improved meansfor chilling the milk almost instantly as it is poured into the tank.This object is attained by the provision of an upwardly facing shelf orledge along the top edge of the refrigerated walls, the milk beingdistributed along this ledge and allowed to break over the edge and rundown the refrigerated walls in a thin, even film. By the time the milkhas reached the lower half of the tank wall, it has been chilled tosubstantially the holding temperature of 40 F., and the temperature ofany milk held in the tank from previous milkings is practicallyundisturbed.

In the preferred form of my invention, the ledge or shelf issubstantially horizontal, and the milk is discharged through a nozzle intwo oppositely directed streams that follow the ledge around to theopposite side of the tank, breaking gradually over the edge and runningdown the inside surface of the inner wall. One notable advantage of thismilk distributing arrangement is the ease with which it can be cleaned,in marked contrast to the difficulty of cleaning prior gutter-likedevices having a large number of small holes for discharging streams ofmilk directly against the insidesurface of the inner wall.

Another object of the invention relates to the provision of automaticmeans for protecting the milk against freezing in the event ofmalfunctioning of some part of the system. One of the principal hazardsof operating a refrigerated tank of this type and using water as theliquid medium circulated between the inner and outer walls, is that thewater is apt to freeze up solid in some part of the fluid passage,thereby stopping-the circulation of the water and endangering the milk.I overcome this difliculty by providing a temperature-responsive switchwhich turns on the circulating pump first, and a pressure-responsiveswitch connected into the circulatory system which prevents therefrigerating machine from starting up until the circulation of thewater has become established. The circulating pump is thus set intooperation first by a rise in tempera-ture beyond some predeterminedlevel, and functions to start up the refrigerating machinery as soon asthe free circulation of water indicates that the water passages areclear and everything is in good order.

The foregoing and other objects and advantages of the present inventionwill become apparent to those skilled in the art upon consideration ofthe following detailed description of the preferred embodiment thereof,reference being had to the accompanying drawings, wherein:

Figure 1 is a top plan view of a refrigerated liquid storage tankembodying the principles of my invention;

Figure 2 is a side elevational view of the same;

Figure 3 is an enlarged fragmentary elevational view of a portion of theoutside of the tank, showing the liquid refrigerant lines and thesuction line header;

Figure 4 is a sectional view through the same, taken at 44 in Figure 3;

Figure 5 isanother sectional view through the tank, taken at 5-5 inFigure 3;

Figure 6 is an enlarged, partially cutaway elevational view of themake-up tank and circulating pump, as seen from 66 in Figure 1;

Figure 7 is an elevational view of the make-up tank, as seen from theleft-hand side in Figure 6;

Figure 8 is an enlarged fragmentary horizontal section through the tankwall at the top end of one portion of the refrigerant pipe and at thebottom end of the next portion;

Figure 9 is an enlarged sectional view through I the top corner of thetank, taken at 99 in.

Figure 1 showing the ledge at the top edge of the refrigerated wall andthe nozzle for discharging milk lengthwise along the ledge; and

Figure 10 is a more or less schematic drawing, showing a modified formof the invention adapted for the pasteurization of the milk.

In the drawings, the liquid storage tank is designated in its entiretyby the reference numeral I5 and is seen to comprise inner and outer sidewalls I6 and H, a bottom I8, outer shell is, and base plate 20. Theinner wall [6 and the bottom l8 are preferably fabricated of stainlesssteel for sanitary reasons, although the outer Wall [1 and shell l9 maybe made of common steel or any other suitable material. The tank I5 ispreferably, although not necessarily, cylindrical in shape, with its topend closed by two semi-circular covers 2| which are hinged at 22 to atransversely extending bridge portion 23 extending across the top of thetank from one side thereof to the other. member 23 to one side of centeris an electric motor 24 and gear box 25, which drive a shaft 26extending down into the interior of the tank; said shaft having apropeller 2'! aflixed to the bottom end thereof, which serves to agitatethe milk so that a representative sample of the same can be taken fortests as to butter fat content.

The inner and outer walls l6 and I! are concentric with one another andare spaced apart a short distance, forming a narrow, annular chamber 30,which is closed at its top end by the horizontal flange 3! of an anglemember 32. The outer shell [9 is also concentric with the outer wall I!and is spaced outwardly therefrom a few inches to form a space which isfilled with thermal insulation 34; the shell I9 being welded to thecorner of the angle member 32 flush with the vertical flange 35 thereof.At its bottom end, the chamber 30 is closed by the horizontal flange ofanother angle member 36, the vertical flange of which lies flat againstthe outside surface of the inner wall l6 and is welded thereto. Thejunctions of the walls l6 and I! with the angle members 32 and 36 arewelded in continuous seams, making the chamber 30 water tight. 7

Wrapped helically around the outside surface of the inner wall I6 is arefrigerant pipe 40, the coils of which are preferably spaced apart afew inches from one another, as shown in the drawings, so as to form aspiral passage 4| extending from the bottom end of the chamber 30 toa-point adjacent the top end thereof. The pipe 40 is preferablycontinuous from end to end, and is attached for support to the innerwall [6 only at its extreme ends, such attachment being typicallyaccomplished by welds 42 and 43. Tack welds may be used at other pointsalong the length of the pipe, if necessary, to hold the coils tightlywrapped against the inner wall l6 during, assembly of the tank, but suchtack welds serve no structural function in the completed tank, and it isprimarily the end welds 42 and 43 that provide support for the pipe. Thecoils of pipe 40 bridge the space between the tank walls 16 and I1,thereby separating each turn of the passage 4| from the adjoining turn,and serving as spacers for the walls l6, IT, to hold the same apart whenthe pressure on the outside is greater than the pressure on the inside.

The relatively high rate of heat transfer called for during the peakload periods when warm milk is being poured into the tank necessitatesthe use of a considerable length of refrigerant pipe which for practicalconsiderations, is of Mounted on the bridgerelatively small crosssectional area. The frictional resistance to high velocity fiow of therefrigerant through such a pipe would be excessive if the liquidrefrigerant were fed into the pipe at one end thereof and the suctionlinewere connected to the other end, and in order to reduce thefrictional losses to an acceptable level, I provide means for dividingthe length of refrigerant pipe up into several shorter sections, each ofwhich is separate from the adjoining sections and each having its ownliquid line and suction line. To this end, the interior of the pipe 49is plugged at intervals by pairs of plugs 45 and 46; plug 45 closing thetop end of section 49a, and plug 46 closing the bottom end of section40b. The continuity of the pipe 40 is preserved between sections bymeans of short lengths of blank filler tubing 59 of the same diameter aspipe 49, which are also welded to the plugs 45, 46. The several sectionsof the pipe 49 being thus closed off at their ends by plugs 45, 46, andthe sections being joined by tubing 59, the refrigerant pipe 49 is, ineffect, a single, continuous piece of pipe, which, as mentioned earlier,is attached at its extreme ends to the inner wall I6 by welds 42 and 43.

Connected into the bottom end of each of the short sections of therefrigerant pipe 40 and projecting radially outward therefrom is a shortlength of pipe 5| which is connected at its outer end by an elbow 52 andreducer 53 to a length of small diameter tubing 54; the several lengthsof tubing 54 being brought together and connected by a coupling member55 to a multi-jet thermal-expansion valve 56. The liquid refrigerant isdelivered to the expansion valve 56 through tubing 69 and a liquid line62, the latter being connected to the receiver of a refrigerantcompressor 59 in a manner well understood by those skilled in the art. Amanually controlled shut-off valve 6| between tubing 60 and line 62permits the refrigerant to be shut oif altogether when so desired.

Connected into the top end of each of the short sections of refrigerantpipe 49 is a pipe 65 which is connected by a coupling 66 to one branch61 of a suction line header 1|. The header H is a vertical pipe having acap 12 on its bottom end, and the top end thereof is con nected to thesuction line of the refrigerant compressor 59.

The thermal-expansion valve 56 functions to reduce the fluid pressure ofthe liquid refrigerant and to supply the refrigerant uniformly to theseveral short sections of pipe 40, and is opened or closed by a thermalbulb 13 that is clamped against one side of the suction line header H.When the suction line H becomes colder, the thermal bulb 13 causes theexpansion valve 56 to cut down the supply of liquid refrigerant, andwhen the suction line becomes warmer, the expansion valve 56 is openedwider to allow more liquid refrigerant to enter the pipe 40.

The chamber 30 between the tank walls I 6 and H is filled with water,brine, or anti-freeze solution and is circulated through the passage 4|by a pump 80 which is driven by an electric motor 8| The pump and motorare mounted on a platform 82 projecting outwardly from one side of amake-up tank 83 which is supported, in turn, on a platform 19 projectingoutwardly from the shelf l9 near the bottom edge of the tank. The makeuptank 83 is preferably rectangular in cross-section, and only slightlyshorter than the tank IS; the top end of the make-up tank being justbelow the level of the tank top. The make-up tank 83 is of double-wallconstruction for the greater part of its length, and the space betweenthe walls is filled with insulation 84 so as to minimize the transfer ofheat from the atmosphere to the Water circulating through the passagesof the tank. The inner wall 85 of the make-up tank is open at its topend to the atmosphere, and the bottom end thereof is connected by a pipe86 to the bottom end of the fluid passage 4|. The top end of the fluidpassage 4! is connected by another pipe 99 to the suction side 9| of thepump 89; the pipe 99-entering the top end of the makeup tank 93, thenpassing downwardly through the center thereof, and coming out the otherside of the tank for connection to the pump. The discharge side 92 ofthe pump is connected by a pipe 93 to the interior of the make-up tank83, and a valve 94 is connected into the pipe 93 to enable thecirculation to be blocked at this point, for reasons that will bepointed out hereinafter.

From the foregoing description it will be seen that the circulation ofthe water or brine through the passages 4| is effected by the suction ofthe pump 89 instead of by pressure, as in the usual installation. Theliquid entering the bottom end of the passage 4| is merely drawn fromthe makeup tank 93, which, as explained earlier, is open to theatmosphere and therefore under no pressure. The pressure differencerequired to circulate the water through the passages 4| is thus producedby reducing the pressure at the exit rather than by increasing thepressure at the entrance, with the result that the water within thechamber 30 exerts less pressure against the walls It and I! of the tankwhen the pump 86 is operating than when the pump is at rest. In thepreferred form of the invention, the fluid pressure of the Water withinchamber 39 i reduced to a sub-atmospheric pressure so that the walls I6,IT are pressed together by atmospheric pressure against opposite sidesof the pipe 49. The principal advantage of this arrangement is that itcompletely eliminates the need for tying the two walls together so as toprevent their separation. Another advantage is that a better contactbetween each of the walls I9, I! and the pipe 49 is obtained, with theresult that there is little or no leakage of the water from one turn ofthe pas- 'sage 4| into the adjoining turns thereof.

Mounted on the outside of the make-up tank 83 is a pressure switch 99which is connected by tubing 91 to a T-fitting 99 between the pumpdischarge pipe 93 and valve 94. The switch 96 is connected by electricwires I09 to the motor 99 of the refrigerant compressor 59, andfunctions to prevent the machine from operating until the water iscirculating freely through the tank I5. Thus, if the water within thepassages 4| should freeze up solid, causing the circulation to bestopped or greatly reduced, the change in pressure at the T-fitting 98actuates the switch 96, keeping the refrigerating machine from startingup until the ice has melted and circulation is restored. As soon as thewater is circulating freely, switch 96 turns on the motor 99 of therefrigerating machine.

Figure 9 shows the arrangement whereby warm milk emptied into the tankis distributed evenly around the entire circumference of the tank andcaused to run down the inside surface of the cold inner wall It in athin, even film, so that the milk is chilled down to approximately 40 F.before it reaches any milk in the bottom of the tank held over fromprevious milkings. The milk is conveyed to the tank I5 through a pipe(not shown) which is connected by a suitable coupling to a horizontalbranch IOI of a T-shaped distributor nozzle I02. The other branch I03 ofthe nozzle extends down through a holder I04 on the bridge member 23 andterminates a short distance above the horizontal flange CH of the angleiron 32. The top and bottom ends of the vertical branch I03 of thenozzle are closed by plugs I05 and I06, which are removable to permit abrush to be passed clear through for ease in cleaning. .The bottom plugI06 has a stem I I projecting upwardly from its center, and the top endof the stem passes through a hole in plug I and is threaded to receive awing nut I I I.

Holes II2 are drilled through the bottom end of the branch I03 onopposite sides thereof, and the milk is discharged through these holesin two oppositely directed streams that travel longitudinally along theshelf 3I. The shelf 3| may be flat and substantially horizontal, asshown in Figure 9, or it may be formed with a raised lip or bead alongits inner edge, or inclined in one direction or the other. When theshelf is fiat and horizontal, the stream of milk is carried by its ownmomentum around almost to the other side of the tank; centrifugal forceacting generally to hold the stream back away from the inner edge of theshelf except for a gradual and progressive breaking of the stream overthe edge. With the two streams of milk leaving the nozzle at the propervelocity, the milk breaks uniformly over the inner edge of the shelf 3Iaround the entire circumference of the tank, and runs down therefrigerated wall I6 in a thin, even sheet, giving up its heat almostinstantly and being chilled down to 40 F.

In Figure 10 I show a slightly modified form of my invention, in whichmeans is provided for heating the water in the system, when desired, sothat the milk in the tank can be pasteurized. This pasteurizing featureis no part of the invention claimed herein, but is included for thepurpose of illustrating an alternative way in which the presentinvention can be used to good advantage. Reference is here made to mycopending divisional application filed March 3, 1952, Serial No.274,579, entitled Refrigerated Milk Storage Tank and Pasteurizer,wherein said pasteurizing feature is claimed. To this end, there is aheat exchanger II5 comprising a tank IIG enclosing a chamber III, inwhich is contained a coil II8 of pipe. The bottom end of the coil iscarried out through the side wall of the tank H6 and is connected by apipe I to a T-fitting I2I on the pump discharge pipe 93. A shut-offvalve I22 is connected into the pipe I20, and the valve 94 is moved tothe position shown in FigurelO. The side of valve 94 opposite the pumpis connected by a pipe I23 to a T-fitting I24, on branch of which isconnected by a pipe I25 to the makeup tank 83, and the other branchbeing connected by a pipe I26 to the top end of the coil A boiler I30 islocated below the tank H6 and is connected therewith by pipes I3I, sothat hot water or steam from the boiler is discharged into the chamberII'I, where it heats the water in the pipe coils I I8. Also opening intothe chamber III are two pipes I32 and I33, the former being connected toa source of cold or cool water, such as from a well, and the latterbeing connected to a drain. Shut-off valves I34 permit the pipes I32,I33 to be closed off when they are not needed.

When the tank I5 has been filled to capacity and it is desired topasteurize the milk, the refrigerating machine is shut off and theboiler I30 started up. Valve 94 is then closed and valve I22 is opened.Operation of the pump now causes the water in the system to circulatethrough the coils II8, where it is heated until the milk has been raisedto the pasteurizing temperature of 143 F. The milk is held at thistemperature for 30 minutes, and the boiler I30 is then shut offaltogether. Valves I34 are then opened to flood the chamber III withcold water, which serves to extract a considerable amount of heat fromthe milk in tank I5 and from the water circulating within the doublewalls thereof. As soon as the milk has been cooled down to apredetermined temperature, the valves I34 are closed; valve I22 isclosed; and valve 94 is opened. This restores the circulation of thewater to its original circuit, and the refrigeration machine is thenturned on to chill the milk back down to the holding temperature of 40F.

One extremely advantageous feature of my invention resides in the factthat in case of failure of the refrigeration machine, the milk in thetank I5 can be kept cool enough to delay souring for a considerablelength of time by merely running cold water from a well or other sourcedown into the bottom end of the open make-up tank 83 through a rubberhose or length of pipe. The cold wateris drawn into the chamber 30 andalong the passage M by the pump 80, and after completing the circuit andextracting as much heat as it can from the milk, is discharged into theupper portion of the make-up tank, where it overflows and is allowed torun off as waste. This is, of course, strictly an emergency measure, butits effectiveness has been proved on several occasions whenrefrigeration equipment has failed, and thousands of gallons of milkhave been saved from spoilage.

While I have shown and described in considerable detail what I believeto be the preferred embodiment of my invention, it should be understoodthat such details are merely illustrative, and various changes may bemade in the shape and arrangement of the several parts without departingfrom the broad scope of the invention as defined in the appended claims.

I claim:

1. A refrigerated liquid storage tank comprising inner and outer walls,a refrigerant pipe of considerable length and of relatively small crosssectional area wrapped around said inner wall and serving as a spacerfor said outer wall, said pipe cooperating with said inner and outerwalls to define a continuous passage from one extremity of said tank tothe other, a liquid filling said passage, and means for circulating saidliquid through said passage to effect the maximum transfer of heat fromsaid inner wall to the re frigerant in said pipe, said pipe beingplugged at intervals along its length to form a plurality of shortsections, each of which is separate from its adjoining sections, andeach section having its own liquid and suction lines.

2. A refrigerated liquid storage tank comprising inner and outer walls,a refrigerant pipe wrapped around said inner wall, said pipe cooperatingwith said inner and outer walls to define a continuous passage from oneextremity of said tank to the other, a liquid medium filling saidpassage, and a pump connected at its suction side to the top end of saidpassage, the bottom end of said passage being connected to a source ofliquid at atmospheric pressure, and the said fluid being circulated at apressure below the static head by the suction of said pump.

3. A refrigerated liquid storage tank comprising inner and outer walls,a refrigerant pipe wrapped around said inner wall and attached theretosolely at its ends, said pipe cooperating ,1 with said inner and outerwalls to define a continuous passage from one extremity of said tank tothe other, a liquid filling said passage, and a pump connected at itssuction side to one end of said passage, the other end of said passagebeing connected to a source of liquid at atmospheric pressure, saidfluid being drawn through said passage by the suction of said pump atsaid one end and being maintained at a sub-atmospheric pressure, wherebysaid inner and outer walls are pressed firmly against the opposite sidesof said refrigerant pipe by atmospheric pressure.

4. A refrigerated liquid storage tank of circular horizontalcross-section, said tank having a refrigerant pipe of considerablelength and of relatively small cross sectional area wrapped in helicalcoils around its outer surface and attached thereto solely at its ends,said pipe being interrupted at intervals to form a plurality of shortsections, each of which is separate from its adjoining sections, andeach section having its own liquid and suction lines, said suction linesbeing connected to a common suction line header, and expansion valvemeans for delivering liquid refrigerant uniformly to the liquid line ofeach of said sections.

5. A refrigerated liquid storage tank comprising inner and outer sideWalls, a refrigerant pipe wrapped helically around said inner wall andserving as a spacer to hold said walls apart, said pipe cooperating withsaid inner and outer walls to define a continuous helical passageextending from the lower portion of the tank to the upper portionthereof, a liquid medium filling said passage, a pump having the suctionside thereof connected to the top end of said passage, and a make-uptank associated with said storage tank, the discharge side of said pumpemptying into the upper portion of said make-up tank, and the bottom endof said passage being connected to the bottom end of said make-up tank,said pump being operable to circulate said liquid at a subatmosphericpressure, whereby said walls are pressed firmly against opposite sidesof said refrigerant pipe by atmospheric pressure.

6. A milk storage tank of circular horizontal cross-section, said tankhaving refrigerated side walls, a substantially horizontal shelfextending back from said walls around the top edge thereof, and nozzlemeans for directing streams of milk lengthwise along said shelf inopposite directions, both of said streams of milk following said shelfaround to the other side of said tank and breaking gradually over theedge of the shelf along substantially the entire length thereof, saidstreams of milk being held back away from the inner edge of said shelfby centrifugal force resulting from the circular path of the milk, saidmilk running down over said refrigerated side walls in a thin,relatively even sheet.

7. A refrigerated milk tank comprising an inner wall and an outer wall,a refrigerant pipe wrapped around said inner wall and engaging saidouter wall to define a fluid passage, said pipe being connected to arefrigerating machine, a motordriven circulating pump connected byconduit means to the ends of said passage, and a pressureresponsiveswitch connected into said conduit means, said switch being operable toturn off said refrigerating machine whenever the circulation of water isstopped or unduly impeded by the formation of ice within said passage,said switch permitting said refrigerating machine to be turned on assoon as the ice has melted sufficiently to permit free circulation ofthe water.

8. A refrigerated liquid storage tank having a refrigerant pipe ofconsiderable length wrapped around its outer surface, said pipe havingspaced means separating the same into a plurality of short sections,each of said sections having its own liquid and suction lines, saidsuction lines being connected to a common suction line header, and saidliquid lines being connected to thermal expansion valve means operableto reduce the pressure of the liquid refrigerant and to deliver saidrefrigerant uniformly to each of said sections.

9. A refrigerated liquid storage tank having a plurality of refrigerantpipe sections disposed on its outer surface, each of said sectionshaving a suction line connected to one end thereof and a liquid lineconnected to the other end, means connecting said pipe sections togetherend-to-end, so as to form a continuous member, said suction lines beingconnected to a common suction line header, and said liquid lines beingconnected to a thermal expansion valve, said valve being operable toreduce the pressure of the liquid refrigerant and to deliver saidrefrigerant uniformly to each of said pipe sections.

10. A refrigerated liquid storage tank having a plurality of separate,closed end refrigerant pipe sections wrapped around its outer surface,each of said sections having a suction line connected to one end thereofand a liquid line connected to the other end, tie means connecting thesuction line end of one pipe section to the liquid-line end of the nextsection, so as to form a continuous length of refrigerant pipe, saidcontinuous length of refrigerant pipe being attached solely at its endsto said tank, all of said suction lines being connected to a commonsuction line header, and expansion valve means for delivering liquidrefrigerant uniformly to the liquid line of each of said sections.

FRANK J. ZAMBONI.

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